[clang-tidy] Add new checker: llvm-prefer-isa-or-dyn-cast-in-conditionals

Summary:
Looks at conditionals and finds cases of ``cast<>``, which will
assert rather than return a null pointer, and ``dyn_cast<>`` where
the return value is not captured. Additionally, finds cases that
match the pattern ``var.foo() && isa<X>(var.foo())``, where the
method is called twice and could be expensive.

.. code-block:: c++

  // Finds cases like these:
  if (auto x = cast<X>(y)) <...>
  if (cast<X>(y)) <...>

  // But not cases like these:
  if (auto f = cast<Z>(y)->foo()) <...>
  if (cast<Z>(y)->foo()) <...>

Reviewers: alexfh, rjmccall, hokein, aaron.ballman, JonasToth

Reviewed By: aaron.ballman

Subscribers: xbolva00, Eugene.Zelenko, mgorny, xazax.hun, cfe-commits

Tags: #clang-tools-extra, #clang

Differential Revision: https://reviews.llvm.org/D59802

llvm-svn: 359142

1 files changed, 3 insertions, 0 deletions

diff --git a/clang-tools-extra/clang-tidy/llvm/LLVMTidyModule.cpp b/clang-tools-extra/clang-tidy/llvm/LLVMTidyModule.cpp
index f5242685c06..fb7b52a3815 100644
--- a/clang-tools-extra/clang-tidy/llvm/LLVMTidyModule.cpp
+++ b/clang-tools-extra/clang-tidy/llvm/LLVMTidyModule.cpp
@@ -12,6 +12,7 @@
 #include "../readability/NamespaceCommentCheck.h"
 #include "HeaderGuardCheck.h"
 #include "IncludeOrderCheck.h"
+#include "PreferIsaOrDynCastInConditionalsCheck.h"
 #include "TwineLocalCheck.h"
 
 namespace clang {
@@ -25,6 +26,8 @@ public:
     CheckFactories.registerCheck<IncludeOrderCheck>("llvm-include-order");
     CheckFactories.registerCheck<readability::NamespaceCommentCheck>(
         "llvm-namespace-comment");
+    CheckFactories.registerCheck<PreferIsaOrDynCastInConditionalsCheck>(
+        "llvm-prefer-isa-or-dyn-cast-in-conditionals");
     CheckFactories.registerCheck<TwineLocalCheck>("llvm-twine-local");
   }
 };